1. Field of the Invention
The present invention relates to a chemical composition that dissolves a sample taken from semiconductor device fabrication equipment made of heat-resistant and acid-resistant materials including silicon carbide, quartz, and zirconium, and to a method of analyzing contaminants on the equipment sample after the sample is dissolved in the chemical composition.
2. Description of the Related Art
Quartz, which has high heat-resistance and acid-resistance, is normally used to make semiconductor device fabrication equipment, such as the tube in which the semiconductor device is fabricated using a high temperature processing gas, and the boat that is introduced into the tube for holding a plurality of wafers to be processed. However, the process conditions cause structural disorder in the crystal of the quartz so that the shape of the boat is distorted and the plurality of wafers housed therein are damaged.
To avoid the problems encountered by using quartz, semiconductor device fabrication equipment has recently been made of silicon carbide which has relatively better heat-resistance and acid-resistance than the quartz and a more stable structure.
Contaminants originating from the processing gas induced into the tube, or by-products of the reaction of the processing gases, adhere to the surface of semiconductor device fabrication equipment. These contaminants include boron, aluminum, and antimony, etc. Contaminants can cause shorts in the fabricated semiconductor device, or cause the device to malfunction due to variances in the operation voltage resulting from contamination on wafers that were prepared inside contaminated equipment.
Therefore, there is a great need for quantitative and qualitative methods to analyze the contaminants adhered to semiconductor device fabrication equipment. There are two ways to analyze such contamination: by non-destructive analysis and by destructive analysis.
The non-destructive method employs techniques such as GD-MS (Glow Discharge-Mass Spectrometer), GD-OED (Glow Discharge-Optical Emission Spectrometer), XRF (X-Ray Fluorescence), ICP-MS (Inductively Coupled Plasma-Mass Spectrometer), Laser, etc. Although the non-destructive methods permit analysis without obtaining a sample of the material, such as the boat or tube on which the contaminants have formed, they are not highly accurate.
Destructive methods which include Atomic Absorption Spectroscopy or Inductively Coupled Plasma-type Atomic Emission Spectroscopy, are more accurate but they require analysis of a sample of the semiconductor equipment on which the contaminants have adhered.
The Atomic Absorption Spectroscopy method operates on the theory that the amount of radiation absorbed by a sample that absorbs radiation having a specific wavelength, is proportional to the concentration of the atoms contained in the sample which is being analyzed. Therefore, after an object to be analyzed is dried inside a high temperature graphite reactor, ashed, and atomized, radiation having a specific wavelength which can be absorbed by targeted sample atoms, is irradiated onto the sample. The absorbance of radiation indicates the degree to which the targeted atoms inside the sample absorb the radiation, and provides a way to quantitatively and qualitatively analyze the kinds and the amount of the contaminants adhered to the sample.
Inductively Coupled Plasma-type Atomic Emission Spectroscopy requires generation of a plasma by supplying argon gas to the processing chamber and applying high-frequency voltage to the induction coil provided outside the processing chamber. Then, a reference solution is supplied to the stabilized plasma which causes the excited atom or ion of the targeted element in the solution to emit radiation. The radiation is analyzed through the spectroscope, and the kinds and the amount of the contaminants in the sample are quantitatively and qualitatively analyzed.
Analyzing contaminants using a destructive method is additionally complicated by the fact that the structure of the silicon carbide used to make the semiconductor device fabrication equipment is so stable. Silicon carbide is not dissolved by known chemical compositions and the silicon element of the silicon carbide also acts as matrix so that exact quantitative and qualitative analysis of the contaminants cannot be done.